1. Field of the Invention
The present invention relates to a high-pressure fuel pump installed in a high-pressure fuel supply assembly used in a cylinder-injected engine, for example.
2. Description of the Related Art
FIG. 5 is a block diagram of a conventional high-pressure fuel supply assembly 100, and FIG. 6 is a cross section thereof. This high-pressure fuel supply assembly 100 includes: a low-pressure damper 2 for absorbing surges in low-pressure fuel, the low-pressure damper 2 being connected to a low-pressure fuel intake passage 1 through which flows low-pressure fuel from a low-pressure fuel pump (not shown); a high-pressure fuel pump 3 for pressurizing low-pressure fuel from the low-pressure damper 2; a high-pressure damper 5 for absorbing surges in the high-pressure fuel flowing through a high-pressure fuel discharge passage 4 connected to the high-pressure fuel pump 3; and a check valve for improving the starting of an engine by maintaining fuel in delivery pipes 8 at high pressure even when the engine is stopped, the check valve being disposed between the high-pressure damper 5 and a fuel supply port 7 and opening when the fuel pressure on the delivery pipe 8 side is lower than the fuel pressure on the high-pressure damper 5 side. Moreover, in the drawings, 17 is a passage connecting to a high-pressure regulator (not shown) from between the fuel supply port 7 and the delivery pipe 8.
The above low-pressure damper 2 is mounted in a first recess 10a in a casing 10. The low-pressure damper 2 includes: a cylindrical holder 14; a base 13 having a ball 11 disposed in a bore 12; and a metal bellows 15 disposed inside the holder 14.
The above high-pressure fuel pump 3 includes: a valve assembly 20 for opening and closing the low-pressure fuel intake passage 1 and the high-pressure fuel discharge passage 4; and a high-pressure fuel supply body 21 for pressurizing low-pressure fuel and discharging it into the high-pressure fuel discharge passage 4.
FIG. 7 is a cross section of the valve assembly 20, the valve assembly 20 being composed of a first plate 22, a second plate 23, and a thin, flat valve main body 19 positioned between the first and second plates 22 and 23. A first fuel inlet 24 connected to the low-pressure fuel intake passage 1 and a first fuel outlet 25 connected to the high-pressure fuel discharge passage 4 are formed in the first plate 22, the inside dimensions of the first fuel outlet 25 being larger than the inside dimensions of the first fuel inlet 24. A second fuel inlet 26 having inside dimensions larger than those of the first fuel inlet 24 and a second fuel outlet 27 having inside dimensions smaller than those of the first fuel outlet 25 are formed in the second plate 23. The valve main body 19 is provided with an intake-side tongue 28 interposed between the first fuel inlet 24 and the second fuel inlet 26, and a discharge-side tongue 29 interposed between the first fuel outlet 25 and the second fuel outlet 27.
The high-pressure fuel supply body 21 includes: a casing 10 housing the valve assembly 20 inside a second recess 10b; a cylindrical sleeve 30 housed in surface contact with the second plate 23 of the valve assembly 20; a piston 33 slidably inserted inside the sleeve 30 forming a fuel pressurization chamber 32 in cooperation with the sleeve 30; and a first spring 36 disposed between a recessed bottom surface 34 of the piston 33 and a holder 35, the spring 36 applying force to the piston 33 in a direction which expands the volume of the fuel pressurization chamber 32.
The high-pressure fuel supply body 21 also includes: a housing 37 fitted over the sleeve 30; a ring-shaped securing member 38 securing the valve assembly 20, the sleeve 30, and the housing 37 inside the second recess 10b of the casing 10 by fitting over the housing 37 and engaging the second recess 10b of the casing 10 by a male thread portion formed on an outer circumferential surface of the securing member 38; a metal bellows 40 disposed between the housing 37 and a receiving portion 39; a second spring 41 compressed and disposed around the outside of the bellows 40 between the housing 37 and a holder 42; and a bracket 43 disposed to surround the second spring 41, the bracket 43 being secured to the casing 10 by a bolt (not shown).
The high-pressure fuel supply body 21 also includes: a tappet 44 slidably disposed in a slide bore 43a in an end portion of the bracket 43; a pin 45 rotatably suspended in the tappet 44; a bush 46 rotatably disposed on the pin 45; and a cam roller 47 rotatably disposed on the bush 46, the cam roller 47 contacting a cam (not shown) secured to a cam shaft (not shown), following the shape thereof, and reciprocating the piston 33.
The above high-pressure damper 5 is screwed into a third recess 10c in the casing 10. The high-pressure damper 5 includes: a first case 50; a second case 51 disposed opposite the first case 50, the second case 51 forming a space in cooperation with the first case 50; and a thin, flat disk-shaped stainless steel diaphragm 54 dividing the space into a back-pressure chamber 52 charged with high-pressure gas and a buffer chamber 53. The diaphragm 54 moves so that the pressure of the fuel flowing into the buffer chamber 53 from the high-pressure fuel discharge passage 4 is equalized with the pressure of the high-pressure gas in the back-pressure chamber 52, thereby changing the volume inside the buffer chamber and absorbing surges in the fuel in the high-pressure fuel discharge passage 4.
In a high-pressure fuel supply assembly 100 having the above construction, the piston 33 is reciprocated by the rotation of the cam secured to the cam shaft of an engine (not shown) by means of the cam roller 47, the bush 46, the pin 45, and the tappet 44.
When the piston 33 is descending (during the fuel intake stroke), the volume of the inside of the fuel pressurization chamber 32 increases and the pressure inside the fuel pressurization chamber 32 decreases. When the pressure inside the fuel pressurization chamber 32 falls below the pressure at the first fuel inlet 24, the intake-side tongue 28 of the valve main body 19 bends towards the second fuel inlet 26, allowing fuel in the low-pressure fuel supply passage 1 to flow through the first fuel inlet 24 into the fuel pressurization chamber 32.
When the piston 33 is ascending (during the fuel discharge stroke), the pressure inside the fuel pressurization chamber 32 increases, and when the pressure inside the fuel pressurization chamber 32 rises above the pressure at the first fuel outlet 25, the discharge-side tongue 29 of the valve main body 19 bends towards the first fuel outlet 25, allowing fuel in the fuel pressurization chamber 32 to flow through the first fuel outlet 25 and the fuel discharge passage 4 into the high-pressure damper 5, where fuel pressure surges are absorbed. High-pressure fuel is then supplied to the delivery pipes 8 via the check valve 6 and the fuel supply port 7, and thereafter supplied to the fuel injection valves 9, which inject fuel into each of the cylinders (not shown) of the engine.
In the high-pressure fuel pump 3 of the high-pressure fuel supply assembly 100 of the above construction, the housing 37, the sleeve 30, and the valve assembly 20 are held inside the second recess 10b by the securing member 38. Because the securing member 38 presses on an outer circumferential portion of the housing 37, the valve assembly 20 is subjected to a large load from the casing 10 at an outer circumferential portion of the valve assembly 20, and to an extremely small load at a central portion of the valve assembly 20. FIG. 6 shows the distribution of the load at that time, and it can be seen that the load increases radially outwards.
At the central portion of the valve assembly 20, the pressure bearing on the valve assembly 20 is extremely low, and during the fuel intake stroke, when the load acting on a peripheral portion 27a of the second fuel outlet 27 on the second plate 23 through the discharge-side-tongue 29 at the mouth of the first fuel outlet 25 corresponds to the cross-sectional area of the mouth multiplied by the discharge pressure, there is a risk that the second plate 23 will be deformed by the load towards the piston 33 in the vicinity of the central portion where the pressure bearing on the peripheral portion 27a is extremely low.
Similarly, during the fuel discharge stroke, when the load acting on a peripheral portion 24a of the first fuel inlet 24 on the first plate 22 through the intake-side tongue 28 at the mouth of the second fuel inlet 26 due to the high pressure in the fuel pressurization chamber 32 corresponds to the cross-sectional area of the mouth multiplied by the pressure inside the fuel pressurization chamber, there is a risk that the first plate 22 will be deformed by the load towards the high-pressure damper 5 in the vicinity of the central portion where the pressure bearing on the peripheral portion 24a is extremely low.
When the second plate 23 or the first plate 22 bend in this manner, even though there should not normally be any gap between the second plate 23 and the discharge-side tongue 29 during the fuel intake stroke, a gap forms between the second plate 23 and the discharge-side tongue 29 in the vicinity of the central portion where the bearing pressure is extremely low. Similarly, even though there should not normally be any gap between the first plate 22 and the intake-side tongue 28 during the fuel discharge stroke, a gap forms between the first plate 22 and the intake-side tongue 28 in the vicinity of the central portion where the bearing pressure is extremely low. Consequently, when the discharge pressure is high, one problem has been that fuel leaks out from between the second plate 23 and the discharge-side tongue 29 during the fuel intake stroke, and out from between the first plate 22 and the intake-side tongue 28 during the fuel discharge stroke, dramatically reducing volumetric efficiency {(the actual amount of fuel discharged into the high-pressure fuel discharge passage 4 from the fuel pressurization chamber 32 during one stroke of the piston 33)/(the cross-sectional area of the piston 33.times. the stroke distance)}. Another problem has been that due to the formation of the above gaps, fretting occurs in places other than the intake-side tongue 28 and the discharge-side tongue 29 of the valve main body 19, such as between elements of the casing 10, the valve assembly 20, and the sleeve 30, giving rise to fuel leaks from gaps there and reducing the discharge flow.